Currently, a touch screen has been spread quickly from being used in a small minority commercial market, such as an ATM (automatic teller machine) in a bank and an industrial control computer to being applied in a mass consumption electronic apparatuses, such as mobile phones, PDA (personal digital assistant), GPS (global positioning system), PMP (such as MP3 or MP4) and panel computers. The touch screen, which has advantages of simple, convenient and humanized touch operations, will be a best human-computer interaction interface and be widely applied in portable apparatus.
A capacitance touch screen is generally divided into two types: self-capacitance type and mutual-capacitance type. FIG. 1 shows a structure of a conventional self-capacitance type touch screen. The self-capacitance type touch screen comprises a plurality of induction units 100′ and 200′ which have a diamond structure and are located in two different layers. A scanning is performed along an X axis and a Y axis respectively, and if a capacitance variation of a certain intersection point exceeds a predetermined range, the intersection point is made as a touch point. Although a linearity of the self-capacitance type touch screen is good, ghost touch points still appear frequently, and thus it is difficult to realize a multipoint touch. In addition, since a double-layer screen is used, the structure is complicated and the cost is increased. Moreover, under a condition of a slight capacitance variation, the diamond structure may cause a coordinate drift, that is, the diamond structure may be easily affected by an external factor.
FIG. 2 shows a structure of another conventional self-capacitance type touch screen. The self-capacitance type touch screen uses a triangular screen structure. The self-capacitance type touch screen comprises: a substrate 300′, a plurality of triangular induction units 400′ disposed on the substrate 300′, and a plurality of electrodes 500′ connected with the triangular induction units 400′ respectively. A single-end detection is performed for the conventional triangular induction unit, that is, the detection is performed only from one direction of the induction unit. Although the self-capacitance type touch detecting assembly has a simple structure, an induction capacitance of the screen is not optimized, so that the capacitance variation is small, thus reducing a signal-to-noise ratio. In addition, because each induction unit has a triangular shape, when the figure moves horizontally, the contact area may not increase linearly, thus causing the deviation of the X coordinate and a poor linearity accordingly.
Induction wires of the self-capacitance type touch screen are made into substantially triangular rings from conductive materials. Two adjacent induction wires are disposed opposite to each other. A number of electrodes required in a given region depends on a width of each induction wire and a distance between every two adjacent induction wires. A number of the induction wires may influence a complexity of a relative disposition between the induction wires and an available resolution of a given point. Meanwhile, the available resolution of a given point may also be influenced by a marginal shape of each induction wire. As shown in FIG. 2, since a contact face between a finger 600′ and a screen is substantially an ellipse and an influence of a slope on graphic design is taken into account, by analyzing from the viewpoint of physics, when the ellipse moves on the screen, an area of a part of the triangular induction unit 400′ covered by the finger 600′ may not vary stably linearly. Similarly, an induction capacitance of the part of the triangular induction unit 400′ covered by the finger 600′ may not vary stably and linearly.
In addition, because the capacitance variation of a conventional capacitance induction unit is small to a femtofarad order of magnitude, a measure circuit needs to satisfy a higher requirement because of an existence of a stray capacitance. Moreover, because the stray capacitance may vary because of many factors, such as temperature, position, and distribution of internal and external electric field, the stray capacitance may interfere with or even bury a tested capacitance signal. In addition, for a single-layer capacitance, because the induction capacitance may be seriously interfered by an influence of a level signal Vcom, which is used for preventing a liquid crystal of a LCD screen from aging.